
//
// Copyright 2009 Arne Halvorsen (arne.halvorsen@gmail.com)
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

// Project page: http://code.google.com/p/mf4j/

//
// 091116 - aha42 - Starts in line change tracking.
// 091121 - aha42 - Added project page link (google code) to header comment.
// 091208 - aha42 - computeText now throws IllegalStateException, a run time
//                  exception and not IOException.
//

package org.aha.mf4j.util;

import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

/**
 * <p>
 *   Utility method to compute MD5 hash.
 * </p>
 * @author Arne Halvorsen (aha42).
 */
public final class MD5
{
  private MD5(){} // Utility pattern dictates private constructor.
  
  private static String convertToHex(byte[] data) 
  {
    StringBuilder buf=new StringBuilder();
    for (int i=0; i<data.length; i++)
    {
      int halfbyte=(data[i]>>>4)&0x0F;
      int two_halfs=0;
      do 
      {
        if ((0 <= halfbyte) && (halfbyte <= 9))
          buf.append((char) ('0' + halfbyte));
        else
          buf.append((char) ('a' + (halfbyte - 10)));
        halfbyte = data[i] & 0x0F;
      } 
      while(two_halfs++ < 1);
    }
    return buf.toString();
  }
   
  /**
   * <p>
   *   Computes MD5 hash.
   * @param text Text to compute hash for.
   * @return Hash.
   * @throws IOException If fails.
   */
  public static String compute(String text)   
  {
    try
    {
      MessageDigest md;
      md=MessageDigest.getInstance("MD5");
      byte[] md5hash=new byte[32];
      md.update(text.getBytes("UTF-8"), 0, text.length());
      md5hash=md.digest();
      return convertToHex(md5hash);
    }
    catch (NoSuchAlgorithmException nax)
    { 
      RuntimeException rx=new IllegalStateException();
      rx.initCause(rx);
      throw rx;
    }
    catch (UnsupportedEncodingException uex)
    { 
      RuntimeException rx=new IllegalStateException();
      rx.initCause(uex);
      throw rx;
    }
  }
  
}
